This invention relates to insulated pipe and a method for making such pipe.
Piping systems for conducting high and low temperature fluids generally include an inner carrier pipe for conducting the fluid, a layer of insulation surrounding the O.D. of the carrier pipe, and a tubular outer jacket or shell around the insulating layer. The insulation provides a low thermal conductivity layer around the carrier pipe to maintain steady temperatures within the fluid being conducted. The outer jacket or shell protects the insulation against water absorption.
In one prior art method of making insulated pipe, a polyvinyl chloride outer shell is extruded around the carrier pipe, and a foam insulating layer is injected into the annulus between the extruded shell and the carrier pipe in a continuous process. This process is time consuming and it requires costly equipment to carry out the continuous process. Moreover, the extrusion process limits the pipe to the use of thermoplastics for the outer shell which are limited in their temperature capabilities.
In another prior art method of making insulated pipe, the insulation layer is made from fiberglass felt. It is common practice to increase the density of the fiberglass felt by impregnating the glass fibers with resin, and then compacting the felt within the heated mold to cure the resin. This produces a rigid fiberglass layer of the desired shape and high density. The increased density is desirable because of the added thermal resistance to heat flow desired for a given thickness of insulation. The rigid fiberglass layer usually is molded in semi-circular shaped half shell blocks which are attached to the O.D. of the carrier pipe. The outer jacket or shell is then placed around the fiberglass blocks. It is difficult to slide a rigid tubular outer shell lengthwise along the O.D. of the rigid fiberglass blocks and have the insulating layer completely fill the annular space between the carrier pipe and the shell. This problem can be avoided by extruding an outer shell around the insulation layer, but this has the disadvantages of being costly, time consuming, and temperature-limiting as discussed above.